A development is carried forward to apply a magnetic resistance device showing a tunnel magnetic resistance effect (TMR effect) to a magnetic random access memory (MRAM) and a reproduction magnetic head of a high density magnetic recording apparatus. The TMR effect is a kind of magneto-resistance effect. As the magneto-resistance effect, a giant magnetic resistance effect (GMR effect) is known in addition to the TMR effect. However, the TMR effect which shows the magneto-resistance effect larger than the giant magnetic resistance effect (GMR effect) is preferable in application to MRAM and the reproduction magnetic head.
As shown in FIG. 1, the magnetic resistance device showing the TMR effect is typically composed of an anti-ferromagnetic layer 101, a pinned ferromagnetic layer 102, a tunnel barrier layer 103 and a free ferromagnetic layer 104. For example, the anti-ferromagnetic layer 101 is formed of anti-ferromagnetic material such as Fe—Mn and Ir—Mn. For example, the pinned ferromagnetic material 102 and the free ferromagnetic layer 104 are formed of ferromagnetic material such as permalloy and have spontaneous magnetizations, respectively. The direction of the spontaneous magnetization of the pinned ferromagnetic material 102 is fixed through an exchange coupling operation received from the anti-ferromagnetic layer 101. A direction of the spontaneous magnetization of the free ferromagnetic layer 104 is reversible into a direction parallel or anti-parallel to that of the spontaneous magnetization of the pinned ferromagnetic material 102. The tunnel barrier layer 103 is formed of non-magnetic substance which is an insulator like alumina (Al2O3). The thickness of the tunnel barrier layer 103 is thin to the extent that tunnel current flows in the direction perpendicular to the surface of tunnel barrier layer 103 and typically is 1 to 3 nm. The magnetic resistance device having such a structure is sometimes called a magnetic tunnel junction (MTJ). The structure of the magnetic resistance device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 4-103014), and U.S. Pat. No. 5,650,958.
The resistance of the magnetic resistance device changes due to the TMR effect in accordance with a relative relation of direction of the spontaneous magnetization of the pinned ferromagnetic layer 102 and that of the spontaneous magnetization of the free ferromagnetic layer 104. In an MRAM which contains magnetic resistance devices, the change of the resistance of the magnetic resistance device is used for the detection of stored non-volatile data. In the magnetic head which contains the magnetic resistance device, the change of the resistance of the magnetic resistance device is used for the detection of an external magnetic field.
A technique to improve the characteristic of the magnetic resistance device showing the TMR effect is disclosed in U.S. Pat. No. 5,966,012. In the magnetic resistance device showing the TMR effect, it is important to decrease the magnetostatic interaction between the ferromagnetic layers. The above U.S. Pat. No. 5,966,012 discloses the technique, in which each of a pinned ferromagnetic layer and a free ferromagnetic layer contains two ferromagnetic layers and a non-magnetic layer interposed between the ferromagnetic layers. Such a structure effectively decreases the magnetostatic interaction between the ferromagnetic layers. It is described in the U.S. Pat. No. 5,966,012 to use a Ru layer as the non-magnetic layer.
A problem of the magnetic resistance device utilizing the TMR effect is heat resistance. A method of manufacturing the MRAM and the magnetic head contain a heat-treatment process. For example, the method of manufacturing the MRAM contains processes in which the magnetic resistance device is heated to a temperature in a range of 300° C. to 400° C., such as a process of forming an interlayer insulating film, a hydrogen sintering process of a transistor, and a packaging process. When a high temperature is applied to the magnetic resistance device, the material of the anti-ferromagnetic layer 101 diffuses into the tunnel barrier layer 103 and the free ferromagnetic layer 104 through the pinned ferromagnetic layer 102, to degrade the characteristic of the magnetic resistance device. Especially, when the anti-ferromagnetic layer 101 is formed of the anti-ferromagnetic material which contains manganese like Ir—Mn and Pt—Mn, the problem of the degradation of the magnetic resistance device is more important. Manganese has the nature easy to diffuse, and it is confirmed by a composition analysis and a section observation that manganese possibly reaches the tunnel barrier layer 103 and the free ferromagnetic layer 104 from the anti-ferromagnetic layer 101 in a short time.
A structure of the magnetic resistance device to effectively restrain the diffusion of Mn contained in the anti-ferromagnetic layer is disclosed in Japanese Laid Open Patent Application (JP-P2002-158381A). The magnetic resistance device has an anti-ferromagnetic layer which contains Mn, a magnetization fixing layer formed on the anti-ferromagnetic layer, a tunnel barrier layer formed on the magnetization fixing layer and a magnetization free layer formed on the tunnel barrier layer. The magnetization fixing layer has a structure in which an insulating layer or an amorphous magnetic layer is put between first and second ferromagnetic layers.
Another problem of the magnetic resistance device utilizing the TMR effect is that magnetic field necessary to reverse the direction of the spontaneous magnetization of the free ferromagnetic layer 104 is asymmetry with respect to the direction to be reversed due to the Neel effect (orange peel effect). The Neel effect is caused in the structure of two ferromagnetic layers and a non-magnetic layer interposed between the ferromagnetic layers and it depends on the non-flatness of each of the two ferromagnetic layers. The Neel effect combines the two ferromagnetic layers ferromagnetically and turns the directions of the spontaneous magnetizations of the two ferromagnetic layers to the same direction (in parallel). The Neel effect makes the magnetic field necessary to turn the directions of the spontaneous magnetizations of the two ferromagnetic layers in the anti-parallel direction larger than the magnetic field necessary to turn the directions of the spontaneous magnetizations of the two ferromagnetic layers in parallel. For the reason of the Neel effect, the magnetic field necessary to reverse the direction of the spontaneous magnetization of the free ferromagnetic layer 104 becomes asymmetry. The magnetic resistance device utilizing the TMR effect receives large influence of the Neel effect because the thickness of the tunnel barrier layer 103 interposed between the pinned ferromagnetic layer 102 and the free ferromagnetic layer 104 is very thin.
In conjunction with the above description, a magnetic memory device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-238923). A magnetic device of this conventional example is composed of an insulating layer having a thickness through which a tunnel current can pass, and first and second ferromagnetic films arranged to put the insulating layer between them. A non-magnetic film is inserted in least one of the first and second ferromagnetic films. Or, the magnetic device is composed of granular magnetic films having the small ferromagnetic particles which are dispersed in a dielectric substance matrix and having magnetic coercive force, and a ferromagnetic film arranged closely to the granular magnetism film. Tunnel current flows between the granular magnetic film and the ferromagnetic film. A non-magnetic substance film is inserted into the ferromagnetic film. According to this conventional example, a desired output voltage value can be obtained and the decrease of a magnetic resistance changing percentage is less even if the current value flows into the ferromagnetic tunnel junction element is increased.
Also, a magneto-resistance effect device is disclosed in Japanese Laid Open Patent Application (JP-P2000-156530A). The magneto-resistance effect device of this conventional example is composed of a first magnetic layer, the direction of whose magnetization changes due to an external magnetic field, a second magnetic layer, a direction of whose magnetization is fixed, and a non-magnetic layer provided between the first and second magnetic layers. The magneto-resistance effect device is further composed of a metal barrier layer provided adjacent to the first magnetic layer and an electron reflection layer provided adjacent to the metal barrier layer and containing at least one selected from the group consisting of oxide, nitride, carbide, fluoride, chloride, sulfite and boride. Moreover, a metal lower layer and a crystal growth control layer may be provided. According to this conventional example, a long-term reliability is improved and an initial characteristic is also improved.
Also, a magnetic recording medium is disclosed in Japanese Laid Open Patent Application (JP-P2001-76329A). In the magnetic recording medium of this conventional example, a lower film is formed on a non-magnetic substrate. A magnetic film of a granular structure is formed on the lower film by a sputtering method using a target which consists of a mixture of ferromagnetic material and non-magnetic material with the resistance of 106 Ωcm or below, or by a dual sputtering method using a target of a ferromagnetic material and a target of non-magnetic material with the resistance 106 Ωcm below, and then a protection film is formed on it. According to this conventional example, the magnetic film of the granular structure with a good smoothness is provided such that friction with the magnetic head is small, and the magnetic recording medium is excellent in the durability.
Also, a magnetic head having a spin valve-type magnetic sensor is disclosed in Japanese Laid Open Patent Application (JP-P2001-101622A). The magnetic head of this conventional example has a laminate structure of a ferromagnetic fixed layer, a non-magnetic intermediate layer, and a soft magnetic free layer. The direction of the magnetization of the ferromagnetic fixed layer is fixed to a magnetic field sensed by an exchange coupling section formed directly on the whole surface with an anti-ferromagnetic film or a hard magnetic layer film. The direction of the magnetization of the soft magnetic free layer turns in accordance with an external magnetic field, and the magneto-resistance effect is caused based on change in a relative angle between the direction of the magnetization of the soft magnetic free layer and the direction of the magnetization of the ferromagnetic fixed layer. A pair of electrodes is provided to detect the change of the resistance. The ferromagnetic fixed layer is composed of a laminate layer of a first ferromagnetic film, a non-magnetic insertion layer and a second ferromagnetic film. The first ferromagnetic film and the second ferromagnetic film have sufficiently large ferromagnetic coupling to the magnetic field to be sensed through the non-magnetic insertion layer. The directions of the magnetizations of the first ferromagnetic film and the second ferromagnetic film are in parallel and the first ferromagnetic film and the second ferromagnetic film function as a substantially unitary ferromagnetic film. According to this conventional example, a magnetic head is provided to have a high output and a good waveform symmetry in a narrow gap and a narrow track.
Also, a magneto-resistance effect device is disclosed in Japanese Laid Open Patent Application (JP-P2002-94141A). The magneto-resistance effect device of this conventional example is composed of an anti-ferromagnetic layer, a fixed magnetic layer which is formed to contact the anti-ferromagnetic layer and in which the direction of its magnetization is fixed by exchange anisotropic magnetic field with the anti-ferromagnetic layer, a free magnetic layer formed through a non-magnetic intermediate layer on the fixed magnetic layer, and a bias layer which turns the direction of the magnetization of the free magnetic layer to a direction intersecting with the direction of the magnetization of the fixed magnetic layer. The anti-ferromagnetic layer and the fixed magnetic which is formed in contact with the anti-ferromagnetic layer are formed of an exchange coupling film. The anti-ferromagnetic layer and the ferromagnetic layer are formed in contact with each other and a exchange coupling magnetic field is generated in the interface between the anti-ferromagnetic layer and the ferromagnetic layer to fix the direction of the magnetization of the ferromagnetic layer a predetermined direction. The anti-ferromagnetic layer is formed of anti-ferromagnetic material which contains an element X (here, X is one or more of Pt, Pd, Ir, Rh, Ru, and Os) and Mn. Crystal grains appear in the section of the anti-ferromagnetic layer in the direction of the film thickness of the exchange coupling film and the crystal grains formed in the ferromagnetic layer are discrete in at least a part in the interface. According to this conventional example, even if a film of PtMn alloy which is the anti-ferromagnetic material excellent in corrosion resistance is used as the anti-ferromagnetic layer, the exchange coupling magnetic field can be made small in accordance with the state of the crystal grain boundaries.